alfred guy vuozzo , 46 , shot dead brent mcguigan and his son , brendon .
he carried out shooting last august to avenge nine-year-old sister , cathy .
cathy was killed in a car smash involving brent 's father , herbert , in 1970 .
herbert given nine-month sentence for dangerous driving ; has since died .
vuozzo , from prince edward island , said the sentence had ` haunted ' him .
knew victims , who lived near montague , were not involved in fatal crash .
defendant pleaded guilty to first - and second-degree murder in february .
he was jailed for life on monday ; he is not eligible for parole for 35 years .